This invention pertains to the implosive compacting and consolidating of powders (typically particles or flakes) made up, alternatively, either entirely of an amorphous material, or of a mixture of amorphous and nonamorphous materials. The invention is especially suited to practice with amorphous, magnetic, iron-based and related alloys, such as those sold under the name Metglas--a registered trademark of Allied Corporation. More particularly, the invention features a method for such compaction and consolidation performed under the influence of explosives.
For the purpose of explanation herein, a preferred method of practicing the invention is described in conjunction with the manufacture of electromagnetic device components, such as simple magnetic motor stator rings, respecting which the invention has been found to have particular utility.
Amorphous metals and alloys have been produced to date only as ribbons having a limited thickness and width, and as powders in the form of particles or flakes which have been generated from such ribbon. In electromagnetic applications, where such amorphous materials have high utility, uses of the ribbon form have been limited to laminations or configurations which can be constructed from laminate stacks. Uses of powder flakes, resulting from consolidation of powders by conventional powder metallurgy techniques, in the same sorts of settings, are unsatisfactory because temperatures in excess of the crystallization temperatures, and other inducements to crystallization, cause catastrophic loss of properties as a consequence of reversion to the crystalline state from the amorphous or glassy state.
In recent work by one of us, we discovered that the passage of shock waves from an explosive charge driving a metal plate against an assembly of laminated amorphous Metglas ribbon did not cause crystallization to occur, and did not result in loss of important amorphous properties, such as magnetic permeability and hardness. The pressure used in this work was as high as 350 kilobars. This discovery led to the realization, which lies at the focal point of the present invention, that it would be possible to use explosives to compact and consolidate amorphous powders if overheating and interparticle melting could be avoided.
At about the same time as the work just above related, another of us recognized that utilization of materials with very high permeabilities, such as might be attained by the consolidation of amorphous magnetic alloys, or mixtures of magnetic amorphous alloys and other constituents, could provide for significant advances and efficiencies in electromagnetic devices, such as transformers, magnetic amplifiers, sensors and a wide range of motors. Of particular interest in this recognition was the foreseeable concept of utilizing magnetic amorphous materials having broad-band (frequency response) characteristics, and nonsaturation linearity. In particular, through the selection of particular magnetic amorphous materials, and mixtures of these materials and other materials, magnetic properties of an implosively consolidated body could be tailored to suit particular different end circumstances.
Accordingly, an important general object of the present invention is to provide a method for the implosive compacting and consolidating of amorphous or glassy magnetic powders, as well as mixtures of such powders with other materials, into magnetic and/or electromagnetic products, with a precisely given shape, and with retention of the unique and extraordinary properties of such amorphous materials essentially completely preserved in the final products.
An object intimately related to the one just stated is to provide such a method which features special control of pressure and temperature during the act of consolidation, in a manner which assures that the finally consolidated amorphous particles reliably exhibit substantially the same amorphous characteristics as those displayed by the unconsolidated, free amorphous particles which existed in the preconsolidation mass.
Another object of the present invention is to provide a method of the type so far generally outlined which is simple and inexpensive to perform, and which is capable of yielding quite accurately-shaped final products in an infinite variety of preselected configurations.
According to a preferred method of practicing the invention, the same generally involves: assembling a mass of particles, which may include entirely amorphous particles, or alternatively, a mixture of amorphous and nonamorphous particles, to define, in the assembled but unconsolidated state, a chosen configuration for a finally desired solid body; imploding the assembled mass by an external, substantially surrounding explosive force in a manner which bonds the particles in the mass as a unit to form the desired solid body; and during this imploding step, controlling the pressure and temperature which occur in the consolidating mass to assure that recrystallization of the amorphous particles in the mass, and thereby loss of important amorphous characteristics, does not occur.
As was mentioned earlier, through selection of particular amorphous powders or powder mixtures, the finally desired amorphous qualities, such as hardness, wearability, and magnetic permeability, can be selected, with shape in a final product determined easily by the manner in which the particles are first assembled in an unconsolidated mass. By combining with amorphous particles selected nonamorphous particles, such as hard metallic particles, like tungsten or nickel-base super alloy particles, or hard compound particles, such as alumina (aluminum oxide), tungsten carbide, titanium carbide, boron nitride, or mixtures of some of these, other important characteristics, such as mechanical or structural characteristics, in the finally consolidated body can easily be controlled.
Still a further advantage of the method proposed by the invention is that it is possible, where desirable, to produce, during the act of particle consolidation, a bond between the finally consolidated body and another object. Thus, the method of the invention lends itself to a manufacturing process in which components, one of which it is desired to form with amorphous characteristics, can be assembled during a single implosive consolidation act.
Apparatus for practicing the method of the invention can take a variety of forms. Typically, it includes a container (mold or die or the like) for containing the unconsolidated powder, and for controlling the final shape of the consolidated product. In some instances, where the consolidated powder is to be assembled with another part, this other part may itself function as all or part of the mold for the powder.
Various conventional explosives may be used, as will be explained hereinbelow, with these taking the form typically of powders or slurries which surround the selected mold for the product, with such powder or slurry itself contained in an overall arrangement that allows the body of explosive material to be detonated in such a way that the powder, at the operator's selection, is uniformly, or differentially, consolidated during a consolidation act.
Various other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.